There are known direct-positive light-sensitive materials which provides a positive image by being exposed a pre-fogged silver halide to destroy the fog nuclei. The direct-positive light-sensitive materials of such a type include high-sensitive photographic materials for photograph-taking use, wherein desensitizing dyes are utilized, as described in JP-B-50-3938 (The term "JP-B" as used herein means an "examined Japanese patent publication") and JP-B-50-3937 and photographic materials suitable for processing in illuminated room as described in JP-A-62-234156 (The term "JP-A" as used herein means an "unexamined published Japanese patent application") and JP-A-61-251843.
Hitherto, the fogging of direct-positive light-sensitive materials have been carried out by using a reducing agent after grain formation so as to form reduced Ag nuclei on the grain surfaces to the extent that the resulting fog is photobleachable. In order to achieve high-sensitivity and hard-contrast properties, the extent of fogging is required to be controlled and to be rendered uniform among the grains. However, heightening the sensitivity by reducing the fogging extent is accompanied with problems of making it difficult to provide the intended Dmax and of rendering the gradation soft.
Also, controlling the fogging extent in order to lower the Dmin provides a disadvantage in failing to produce sufficient Dmax and rendering the gradation soft.
Further, direct-positive light-sensitive materials for photograph-taking use are required to have high sensitivity. Therefore, the extent of fogging with a reducing agent should not be enhanced, rendering the Ag nuclei formed minute. Thus, the sensitivity and Dmax of such a raw emulsion tend to vary during the storage in a refrigerator. Even after the emulsion-preparation is completed by adding various additives to such a raw emulsion and a light-sensitive material is produced by coating the completed emulsion on a support, the light-sensitive material thus produced suffers from the defect that it shows variation in sensitivity and Dmax depending upon storage conditions, and so it is inferior in stability, as compared to other general light-sensitive materials.
With respect to direct-positive light-sensitive materials suitable for illuminated room processing, on the other hand, it is necessary to lower their sensitivity, and therefore, the extent of fogging with a reducing agent must be enhanced. This arise a problem that the Ag nuclei formed are hard to be bleached by exposure, and the Dmin thereof is increased.
To solve these problems, the use of a gold compound has been proposed in JP-B-50-3978. However, even when the gold compound is used, the stability of the resulting Ag nuclei is insufficient and the Dmin thereof tends to elevate.
With respect to a development processing, the direct-positive light-sensitive materials have so far been subjected to lith development (using a lith developer, e.g., HS-5, commercial name, a product of Fuji Photo Film Co., Ltd.), but in recent years the trend of processing systems has changed. Specifically, direct-positive light-sensitive materials required to have suitability for rapid processing, such as RAS (which stands for rapid access) processing and hybrid processing (using, e.g., Grandex, produced by Fuji Photo Film Co., Ltd. or Ultratech, produced by Eastman Kodak Co.), as a result, the rapid processing have been desired to provide a high Dmax, a low Dmin, a high contrast, etc. each at the level of the lith processing. With the intention to meet these various requirements, the method of not only providing high sensitivity, high Dmax and high contrast but also ensuring satisfactory stability upon storage in a refrigerator is disclosed, e.g., in JP-A-05-289213. However, since such a method is intended to achieve its aim by first forming stable fogged silver nuclei and then bleaching them, thereby rendering the silver nuclei further minute, it encounters a problem of the storage instability of minute silver nuclei. Thus, it has been strongly desired to develop further advanced arts of stabilizing minute fogged silver nuclei.